The present invention generally relates to an apparatus and a method for removing heat from a turbine shaft and, more specifically, to an apparatus and a method of removing heat from a turbine shaft having foil bearings by utilizing a heat conductive sleeve within the turbine shaft.
Foil bearing rotating machines may require a means of removing heat which may be generated by a shaft rotating within the bearings. Typical designs may use a process fluid such as air, to remove heat generated at the shaft-foil bearing interface. For example, U.S. Pat. No. 3,149,819 to Baumann et al. is directed to utilizing a hollow bush within a hollow cylindrical shaft extending through a gas lubricated bearing to remove heat from the bearing. In Baumann et al., the hollow bush has a higher thermal conductivity than does the hollow shaft, and the hollow bush and the hollow shaft are traversed interiorly thereof by a gaseous coolant.
U.S. Pat. Nos. 4,725,206 and 4,786,238, both to Gaser et al., are each directed to a pliant foil bearing having a plurality of foils extending about a rotatable shaft, a hollow shaft mounted to rotate within the pliant foil bearing with at least a portion of the hollow shaft comprising a bearing journal, and means for circulating a gas through the hollow shaft to cool the shaft.
Other approaches related to removal of heat from turbine shafts include U.S. Pat. No. 3,706,483 to Irwin, which is directed to removing heat from a turbine shaft comprising roller or ball bearings wherein an inner ring of a bearing may be mounted on, or be part of a hollow sleeve which in turn is mounted on a rotating shaft. The interior of the hollow sleeve may be filled with a heat conductive material such as sodium. An end of the hollow sleeve opposite the end at which the inner ring is mounted may comprise cooling fins to dissipate the heat load applied to the turbine shaft.
Conventional methods and apparatus used for removing heat from turbine shafts have disadvantages. Removing heat utilizing a cooling fluid may require utilizing a portion of the turbine output power merely for such cooling, without that portion of the output doing useful work. Accordingly, heat removal utilizing a cooling fluid may reduce the efficiency of the turbine in which this approach is used. Also, utilizing a cooling fluid for heat removal may further require providing a system by which contact between a heat load and the cooling fluid can be accomplished. Such systems may thus add complexity, weight, and cost to the overall system in opposite to design goals.
Use of a hollow sleeve heat sink in direct communication with a bearing may also limit operational parameters available for use in a turbine comprising such a system. In particular, a heat sink material may lack strength and rigidity necessary to maintain the integrity of a system when such a system is operated at rotational speeds consistent with turbine operation.
As can be seen, there is a need for apparatus and methods to remove heat from foil bearing turbine shafts which do not require utilizing a working fluid as a heat exchange medium, and which will allow for system integrity under turbine operational conditions.